Optical data storage disks have gained widespread acceptance for the storage, distribution and retrieval of large volumes of information. Optical data storage disks include, for example, audio CD (compact disc), CD-R (CD-recordable), CD-ROM (CD-read only memory), DVD (digital versatile disk or digital video disk) media, DVD-RAM (DVD-random access memory), and various types of rewritable media, such as magneto-optical (MO) disks, CD-RW (CD-rewritable) and phase change optical disks. Some newer formats for optical data storage disks are progressing toward smaller disk sizes and increased data storage density. In some cases, optical data storage disks are housed within a data storage cartridge.
The process of creating optical data storage disks such as prerecorded disks, recordable disks or rewritable disks begins with a mastering process. For example, the mastering process involves making a master that has a surface pattern that represents encoded data on the master surface. The surface pattern, for instance, may be a collection of features that define master pits and master lands. The mastering process is a relatively expensive process in which a photoresist is coated on a master substrate, exposed to develop a photoresist pattern, and then removed in the exposed or non-exposed regions to define a photoresist pattern.
After creating a suitable master, that master can then be used to make a stamper. The stamper has a surface pattern that is the inverse of the surface pattern encoded on the master. For example, one technique that can be used to create a stamper involves depositing a thin nickel layer on the patterned master surface. Then, in an electroplating process, a nickel structural layer can be uniformly plated onto the nickel coated surface of the master. When the electroplating process is complete, the nickel layers can be collectively removed from the master to form a nickel stamper. This process, however, typically destroys the master.
The stamper can be used to create large quantities of replica disks in a mass production process, such as a rolling bead process or an injection molding process. In a rolling bead process, a bead of photopolymer is positioned between a substrate and the stamper. A roller passes over the substrate and the stamper, dispersing the bead of photopolymer and forcing air to the leading edge of the bead. After the roller has passed over the substrate and the stamper and dispersed the photopolymer, the photopolymer can be cured with ultraviolet (UV) light. The stamper is then peeled back, leaving an inverted image of the stamper within the photopolymer that is cured to the substrate. A reflective material, a phase change material, a magneto-optic material, or the like can then be deposited on the photopolymer. Additional protective layers may also be added.
In an injection molding process, the stamper is inserted within an injection molding tool, and the injection molding tool can be used to injection mold large quantities of molded replica disks. The injection molding tool typically includes mirror blocks positioned on both sides of a mold cavity. The stamper can be vacuum drawn against one of the mirror blocks and hot molten thermoplastic can be injected into the mold cavity. The molten thermoplastic conforms to the mold cavity, defining an inverse of the pattern preserved on the stamper. Upon cooling, the molded thermoplastic may contain the data and tracking information that was encoded on the master and preserved in the stamper. A reflective material, a phase change material, a magneto-optic material, or the like can then be deposited on the molded part according to the desired optical data storage disk format. Additional protective layers may also be added.